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Internal vs External BMS pros and cons

Interested in thoughts regarding Victron batteries with external BMS vs integrated BMS batteries like Battle Born or Victron.

Thanks for Steve Mitchell for his detailed information on a Victron system install.

Have a 2001 Beneteau 361 upgrading from the original Xantrex Freedom 20 to a LiFePO4 & Victron system.

What do you 'lose' or 'gain' by going with the integrated BMS batteries (Battle Born) vs the Victron with external BMS?

Lithium BatteryBMS
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4 Answers
Matthias Lange - DE avatar image
Matthias Lange - DE answered ·

Most batteries with internal BMS have a limited power.
e.g. the 200Ah Victron with internal BMS you have 70A charge/discharge current(100A 10sec peak) and with external BMS 200A recommended discharge(400A max) and 100A recommended charge(400A max) current.

If you only want to use small loads you should be fine with an internal BMS but if you need large loads you should use one with external BMS.

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drlbradley avatar image
drlbradley answered ·

An external BMS does also give you additional options if you needed to switch out your battery and couldn't source one with an internal BMS.

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cpt-pat answered ·

Pros of an external BMS:

1) You can manually top/bottom balance individual cells.

2) An external BMS gives you a lot of useful metrics to measure individual cell health.

3) If a cell fails, you can replace it.

4) They are cheaper (substantially so).

I personally have a mix on my boat. I have three 100 AH Battle Born batteries and two 280 AH batteries with external BMSs. The Battle Borns are on my house bank that serve low current demands. The external BMS/individual cell bank is used for high current demands taken by my inverter powering a microwave oven and induction stovetop, and also serves as a backup to the house bank through a steering diode. If a cell goes soft on that bank, I can replace that individual cell, and on a cost-per-watt-hour basis, the external BMS batteries cost half as much as the Battle Born batteries.

Pros of internal BMS:

1) Environmental protection. Battle Born batteries, for example, are much less likely to be damaged by the salt air and humidity encountered in a marine environment. The delicate BMS circuitry is in a sealed case.

2) Mechanical stability. A well designed drop-in battery is less likely to be damaged by motion and vibration. Be careful though in your selection: I've seen some designs that are really not internally suitable for mobile applications that fail to insulate aluminum cases between cells and some that use foam to stabilize the internal components that are still vulnerable to internal chafing caused by vibration.

3) Warranty. The entire battery may have a warranty.

4) Build quality. The build quality of some drop-in internal BMS batteries can be very high. Although you can achieve the same quality with a DIY battery and an external BMS, you will expend time doing research on lithium battery characteristics (I've invested hundreds of hours reading research papers) and money on proper tools (hydrolytic crimpers, etc.). Some drop-ins are only suitable for stationary applications.


Not a comparison factor of either implementation: power output. In both cases, output will be limited to the capabilities of the cells (usually 1C continuous output or less) and the BMS.



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arghhh40k avatar image
arghhh40k answered ·

Most of the time you don't know what is going on with an internal BMS, there is no external communication and no warnings of issues. The battery just shuts off.


External BMS will usually let you see cell voltages and warnings and you get some notice before a battery just turns off.


Depending on your cruising and how you charge a "battleborn" type drop in battery could turn itself off when full, destroy your alternator and shut down your DC system on your boat. Not ideal if you are running critical systems or can actually be deadly.


You should also check with your insurance carrier as the ABYC has a technical bulletin TE-13 out that requires batteries to have external communication

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Most "drop-in" lithium batteries have a Bluetooth app now to see what's going on in there.